Affiliation: | a Çankaya University, Department of Mathematics and Computer Science, Ögretmenler Cad. 14, 06530 Balgat-Ankara, Turkey b University of Craiova, DAL, Department of Mathematics and Computer Science, Tudor Vladimirescu 26, 200534 Craiova, Romania c Florida Institute of Technology, Department of Mathematical Sciences, Melbourne, FL 32901, USA |